The growth of thin films on substrates by heteroepitaxy is an important manufacturing step in the semiconductor technology. For instance, when native bulk substrates are not available or are too expensive, useful materials are often formed by heteroepitaxy on seed substrates. In the field of light-emitting semiconductor devices or solar cells there is a need to grow heteroepitaxial films of III/N materials on substrates as sapphire or SiC. However, when materials are formed by heteroepitaxy on substrates with a different lattice constants and different coefficients of thermal expansion as compared to the ones of the materials detrimental effects on material quality are caused by misfit compressive or tensile strain and the corresponding generation of dislocations and cracks. Thus, film of materials are formed by heteroepitaxy with a limited thickness such that neither crack nor dislocation occurred in the material. After transfer of the heteroepitaxial films to another substrate these films can, for instance, be used for epitaxial growth of layers used in electronic and opto-electronic, photovoltaic applications. However, thin heteroepitaxial films are strained due to the misfit of lattice parameter and the quality of epitaxial growth or subsequent steps can be deteriorated.
However, presently used methods for the relaxation of strained heteroepitaxial films on low-viscosity layers often not show satisfying results with respect to the suppression of buckling, the formation of cracks, etc. and complete in-plane relaxation can hardly be achieved. Thus, it is a problem underlying the present invention to provide a method for the complete or almost complete relaxation of a strained layer formed above a substrate that avoids or at least alleviates the above-mentioned defects.